BACKGROUND A common and useful approach to pain management is administration of neuraxial opioids. OBJECTIVE Whether addition of fentanyl or meperidine to lidocaine and epinephrine for spinal anesthesia in elective cesarean delivery has any effects on duration of postoperative pain. METHODS This was a clinical trial, conducted on 195 pregnant women candidates for elective cesarean section. All patients were in ASA classes I, and II aged 17-45 years, and were randomly allocated to three groups named as meperidine (P), fentanyl (F), and placebo (S). In the three groups (P, F, and S), 25 mg meperidine, 25 µg fentanyl and 0.5 mL saline with lidocaine and epinephrine were injected into the subarachnoid space for spinal anesthesia, respectively. Perioperative complications and Apgar scores were recorded. Duration of analgesia was measured from the end of operation for 24 hours by using VAS. The first VAS≥4 was recorded as the end of the painless period. Characteristics of sensory and motor block were assessed. Statistical analysis was performed with SPSS software. RESULTS The mean duration of analgesia with meperidine, fentanyl or placebo were 9.46 ± 0.6, 6.27 ± 0.45, 2.06 ± 0.13 hours, respectively (P < 0.0001). There was significant difference between the group P and the other groups. Patients on meperidine had faster, longer and higher sensory block (P < 0.0001) and faster and longer motor block (P < 0.0001). Frequency of sedation in the group F was more than the others (P < 0.026). There was no difference in Apgar scores between the three groups (P < 0.45). CONCLUSIONS Addition of meperidine or fentanyl to lidocaine and epinephrine solution increases the duration of postoperative analgesia in cesarean section. Meperidine is a recommended adjuvant according to longer duration of analgesia and lower complications.